In a conventional steam turbine, a contact-type fin or fitting structural part which partitions spaces under different pressures is provided between two independent stationary parts, so as to suppress leakage of steam. The contact-type fin suppresses leakage of steam by pressing the fin against an opposing stationary part by an elastic member.
In the fitting structural part, a fitting projection formed in a circumferential direction on one stationary part is fitted in a fitting recess formed in the circumferential direction in the other stationary part, to thereby suppress leakage of steam. In this case, leakage of steam is suppressed by that a steam joint surface is formed by pressing the stationary part against the other stationary part by a pressure difference, or that a flow path of steam is narrowed by setting a small gap between the fitting projection and the fitting recess.
Further, in a conventional steam turbine, a groove is formed in the circumferential direction in each of opposing stationary parts, and leakage of steam is suppressed by fitting an annular sealing member having a spherical edge in the respective grooves.
When a space between two independent stationary parts is sealed, the stationary parts move in an axial direction of the turbine rotor (hereinafter referred to as an axial direction) or a radial direction of the turbine rotor (hereinafter referred to as a radial direction) due to a temperature difference between the both stationary parts, a linear expansion coefficient difference, a difference in thermal elongation starting point, and the like. Thus, a positional displacement occurs between the stationary parts.
When a conventional contact type fin is used, if a positional displacement occurs in the axial direction, wear and/or scoring of the fin may occur. The elasticity of the elastic member of the contact-type fin is small, and the range of following a positional displacement in the radial direction has been limited. On the other hand, when the conventional fitting structure is used, if a positional displacement occurs in the axial direction, an excessive stress may occur in the fitting part and the fitting projection may break.
When the sealing structure in which the annular sealing member having a spherical end is fitted in the groove is used, if a positional displacement occurs in the axial direction, the annular sealing member deforms and follows. However, this sealing method has a problem in reliability of the sealing because it uses a contact between a spherical surface and a flat surface, that is, a linear contact. Further, when the annular sealing member deforms, the dividing part of an upper half portion and a lower half portion of the annular sealing member opens, and an uneven deformation may occur across the entire circumference. Thus, a portion where the annular sealing member does not contact a wall surface of the groove may occur, and steam may leak therefrom.